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Warm temperatures shown to slow malaria transmission

A study published on Wednesday in the journal Biology Letters finds that contrary to popular belief, warmer temperatures seem to slow the transmission of malaria-causing parasites by reducing how infectious they are.

While the study at Pennsylvania State University in University Park was done with rodent malaria, the researchers expect the pattern to apply to human malaria and potentially to other mosquito-borne diseases such as dengue fever and West Nile virus, Nature reports.

Studies that predict warmer climates will lead to increased malaria infections typically assume that the disease-causing parasites will develop faster while the ability of the mosquito to acquire, maintain and transmit the pathogen will remain the same. Those studies conclude that as temperature increases, mosquitoes become infectious more quickly, thus increasing malaria transmission. This latest study, however, shows that temperature has a more complex effect, reducing how many parasites become infectious.

“It is a trade-off between parasite development and parasite survival,” Krijn Paaijmans, an entomologist and the study's author, said, according to Nature. “And if you don't factor this in I think you come to the wrong conclusions.”

The researchers incubated mosquitoes infected with rodent malaria-causing Plasmodium yoelii at four different temperatures and then examined the mosquitoes' salivary glands. They found that the parasite developed more rapidly in warmer temperatures, but that there were fewer sporozoites, the infectious form of the parasite.

Parasite development peaked at the highest temperature, though it was not the temperature with the highest risk of malaria.

“[This study] demonstrates the importance of paying attention to parasite ecology,” Sarah Reece, a malaria researcher at Edinburgh University said, according to Nature.

The researchers' next step is to repeat the experiments with human malaria.